In many solid ink printheads, the aperture plate and jet stacks typically consist of stainless steel plates. The aperture plate has an array of small holes, or nozzles, also sometimes referred to as jets, through which the ink exits the jet stack. Stainless steel aperture plates and other plates in the jet stack are being replaced with flexible, polymer layers such as polyimide. In some instances, the polyimide film receives an anti-wetting coating, is bonded to a stainless steel aperture plate, and then a laser ablates the array of apertures into the polyimide film.
Drooling apertures, wetting and adhesion of ink on the printhead front face lead to missing and/or misdirectional jetting along with poor image quality (“IQ”). Drooling apertures weep ink when the internal pressure of the printhead exceeds a particular pressure, typically measured in inches of water. The higher pressure the apertures can maintain without weeping leads to higher jetting latitude and improved performance. Wetting occurs when the front face of the printhead remains wet after printing. Ink that remains on the printhead can block the apertures resulting in missing apertures and misdirectional printing.
Currently, one approach to overcome these issues is to use an active cleaning blade system. The system purges ink from the printhead. Ink purges typically occur after the system detects missing jets and after a power-down when the ink has frozen or solidified, shrunk and drawn air into the system. The ink purge expels contamination, trapped air and clears the apertures, and then the wipers wipe off the front face. With an expected printhead lifetime of 6 years, daily purges can result in roughly 2000 purge and wipe cycles, meaning that in some instances, anti-wetting coating may have to survive and maintain their beneficial properties for over 2000 cycles.
It is desirable for anti-wetting coatings to have high contact angle in order to maintain adequate drool pressure and low slide angle and to maintain an easy clean/self clean feature. This can lead to printhead cartridges with low or no maintenance, high engine reliability and low run cost. It is desirable for anti-wetting coatings to retain these properties after high temperature and pressure conditions that may occur during manufacturing of, for example, a printhead. Unfortunately, some conventional anti-wetting coatings may tend to degrade when exposed to temperatures encountered during typical bonding processes or other high-temperature, high pressure processes encountered during fabrication of inkjet printheads. Further, coatings that do have good thermal and/or ink stabilities may suffer from lower mechanical robustness than may be desirable.
Yet another issue that may arise with anti-wetting coatings is the appearance of a thin layer of oil on the coating surface after high temperature curing processes. While the oil does not seem to directly affect the surface properties and printhead performance, it may cause shelf life issues and problems in packaging and handling. The oil layer can be cleaned from the surface, but this would increase manufacturing complexity and costs.
Novel anti-wetting coatings that can address one or more of the above described problems would be considered an advancement in the art.